The present invention generally relates to the recording and reproducing of a PCM audio signal, and more particularly to a method and apparatus for recording and reproducing a coded audio signal together with a video signal or singly to and from a magnetic tape by a rotary magnetic head type scanner, and still more particularly to a method and apparatus for recording and reproducing a PCM audio signal which is suitable when a sampling frequency for the PCM audio signal and a rotation frequency of the scanner are asynchronous.
The recording and reproducing of a PCM audio signal has been adopted in order to improve the quality of an audio signal accompanied with a video.
For example, an 8 mm video recorder adopts an audio PCM system. A sampling frequency of the audio PCM signal is two times as high as a repetition frequency of a horizontal synchronization signal. It is different from an internationally common sampling frequency (32 kHz, 44.1 kHz or 48 kHz). For example, a sampling frequency of an audio PCM signal in a satellite broadcast is 32 kHz or 48 kHz.
On the other hand, in a MUSE system which is one of transmission systems for a high grade television system, the sampling frequency of the audio PCM signal is 32 kHz or 48 kHz. Thus, if data sampled at the above sampling frequency are to be recorded field by field, the number of data per field includes a fraction In order to resolve this problem, a packet transmission system having a leap field to absorb the excess has been adopted as disclosed in NHK Technical Journal 27-7, page 282.
In a video disk, the PCM audio signal is recorded at the sampling frequency of 44.1 kHz with the same format as that of a compact disk.
However, when the PCM signal is to be recorded by an apparatus such as a video tape recorder which records or transmits the signal discontinuously in time, the following problems arise. First, when a field frequency of a video signal is not an integer multiple of the sampling frequency of the audio signal, the problem described above is encountered in coding. While a solution such as the MUSE system described above has been proposed, there must be a synchronous relationship between the field frequency fv of the video signal or a rotation frequency f.sub.D of a head scanner which rotates synchronously with the field frequency, and the sampling frequency f.sub.s of the video signal. This imposes a limitation to a system application range.
As an apparatus for PCM recording and reproducing only the audio signal by a rotary head type VTR, a consumer PCM encoder/decoder (registered in Sept. 1983) of the Japanese Electronic Industries Association Technical Standard CPZ-105 has been known. A recording and reproducing apparatus in accordance with the above Technical Standard is disclosed in an article "Digital Audio/Video Combination Recorder Using Custom Made LSI's, IC's" presented at the 69th Convention, 1981 May 12-15, Los Angles AES 1791 (B-6), particularly FIGS. 1 and 14. In this article, in the NTSC system, the field frequency f.sub.v and the sampling frequency f.sub.s are divided from the same master clock and they have a relationship of f.sub.s =735 f.sub.v. Accordingly, the number of samples per field is constant at 735.
FIG. 1 of the above article shows a block diagram of a configuration of an apparatus for recording and reproducing sampled PCM signals. An address of a RAM which serves as an interleaving memory is controlled by an address control circuit.
However, when the PCM audio signal is to be recorded together with a video signal by a rotary head helical scan type VTR, and if the video signal is of 525 lines/60 fields Television system, the field frequency (f.sub.v =59.94 Hz) is not an integer multiple of the sampling frequency (f.sub.s =32 kHz, 48 kHz), and the number of blocks per field includes a fraction.
As a result, a block set which is an aggregation of a predetermined number of blocks for processing the signal such as interleaving and deinterleaving is separated between the fields, inconveniently.
A rotary head type digital audio type recorder (R-DAT) for recording only the audio signal has been known and a portion of its specification has been published by "Technical Standard of Rotary Head System (R-DAT)", Dempa Shimbun, Oct. 7, 1985, page 48.
In each of the above cases, it is assumed that the field frequency f.sub.v and the sampling frequency f.sub.s have a certain relationship and there is no discussion for a case where f.sub.v and f.sub.s are not correlated.
In the prior art techniques described above, the sampling frequency of the video signal is not the internationally common sampling frequency, the number of quantized bits is small, and the sampling frequency of the audio signal and the field frequency have a synchronized relationship. Thus, when a video signal from a camera and a digital signal from a compact disk are to be recorded together, it is very difficult to simultaneously record them because the sampling frequencies are different and there is no synchronous relationship between the sampling frequency and the field frequency.
A solution to the above problem has been proposed in British Patent Application No. 423452 field on Sept. 17, 1984 (JP-A-61-73207). Since it has not been published before the present invention, it is not cited herein as prior art.